The present invention relates to a coating film formation method in which sogging etc. do not occur even in an atmosphere of low temperature and high humidity, the orientation of metallic pigment can be controlled particularly in case of using water-borne metallic paint and air-conditioning energy can be largely reduced in a 3-coat-1-bake coating film formation method using a water-borne paint.
Conventionally the coating of an intermediate paint or a topcoat paint was conducted generally in a booth whose inside was usually air-conditioned to suitably control the temperature and humidity. When the temperature and humidity in the booth are not controlled and largely fluctuate, the evaporation velocity of volatile components in the atomized paint particles in spray pattern area changes largely particularly at low temperature and high humidity and the wet film viscosity of the atomized paint particles largely fluctuates and consequently a normal coating film cannot be formed by occurrence of sogging of the wet coat or surface defect of the coating film etc., particularly in case of using a water-borne paint, compared with a solvent-type paint and therefore the air-conditioning control in the above-mentioned booth had to be strictly controlled. Moreover, in case of the coating with a water-borne metallic paint, the controlling tolerance was narrow, because the air-conditioning control influences the orientation of metallic pigment.
In the above-mentioned booth, the temperature and humidity are controlled while supplying and exhausting air, so the energy consumed for air-conditioning in the whole booth is considerable and usually the biggest in the steps in industrial coating line and the reduction of this energy has been an important problem.
The purpose of the present invention is to provide a coating film formation method in which sogging etc. do not occur even in an atmosphere of low temperature and high humidity, the orientation of metallic pigment can be controlled particularly in case of using water-borne metallic paint and air-conditioning energy can be largely reduced in a coating film formation method using a water-borne paint.
The first embodiment of the present invention relates to a coating film formation method characterized by controlling the solid content of the wet coat by an air jet step in which the air, whose temperature and/or humidity are controlled, is jetted from behind the paint nozzle in approximately the same direction as the atomized particles of a thermosetting water-borne color paint (A) move to the surface of the substrate, when said paint is coated, around the spray pattern so that the air touches said pattern, in a coating film formation method in which the thermosetting water-borne color paint (A) is coated on the surface of the substrate, then a thermosetting water-borne paint containing color pigment and/or glittering pigment (B) is coated on said coated surface, and, after predrying as necessary, a thermosetting clear paint (C) is coated and after that said 3-layer coating films of (A), (B) and (C) are simultaneously cured by heating.
The second embodiment of the present invention relates to a coating film formation method characterized by controlling the solid content of the wet coat by conducting a high speed air blow step in which the substrate coated with a thermosetting water-borne color paint (A) is enveloped by air stream and then by an air jet step in which the air, whose temperature and/or humidity are controlled, is jetted from behind the paint nozzle in approximately the same direction as the atomized particles of a thermosetting water-borne paint containing color pigment and/or glittering pigment (B) move to the surface of the substrate, when said paint is coated, around the spray pattern so that the air touches said pattern in a coating film formation method in which the thermosetting water-borne color paint (A) is coated on the surface of the substrate, then the thermosetting water-borne paint containing color pigment and/or glittering pigment (B) is coated on said coated surface, and, after predrying as necessary, a thermosetting clear paint (C) is coated and after that said 3-layer coating films of (A), (B) and (C) are simultaneously cured by heating.